4-{(Z)-2-[(E)-Benzylidenehydrazinylidene]-3,6-dihydro-2H-1,3,4-thiadiazin-5-yl}-3-phenyl-1,2,3-oxadiazol-3-ium-5-olate

The title compound, C18H14N6O2S, exists in trans and cis configurations with respect to the two acyclic C=N bonds [bond lengths = 1.2835 (9) and 1.3049 (9) Å]. The 3,6-dihydro-2H-1,3,4-thiadiazine ring adopts a half-boat conformation. The oxadiazol-3-ium ring makes dihedral angles of 53.70 (4) and 60.26 (4)° with the two phenyl rings. In the crystal, molecules are linked via pairs of intermolecular N—H⋯N hydrogen bonds, generating R 2 2(8) ring motifs, and are further linked via intermolecular C—H⋯O and C—H⋯S hydrogen bonds into a three-dimensional network. The short intermolecular distance between the oxadiazol-3-ium rings [3.4154 (4) Å] indicates the existence of a π–π interaction.


Comment
Sydnones are a class of mesoionic compounds containing a 1,2,3-oxadiazole ring system. A number of sydnone derivatives have shown diverse biological activities such as anti-inflammatory, analgesic and anti-arthritic (Newton & Ramsden, 1982;Wagner & Hill, 1974) properties. Sydnones with heterocyclic substituents at the 4-position are also known to exhibit a wide range of biological properties (Kalluraya & Rahiman, 1997). Encouraged by these reports and in continuation of our research for biologically-active nitrogen-containing heterocycles, a thiadiazine moiety was introduced at the 4-position of the phenylsydnone. A series of thiadiazines were synthesized by the condensation of 4-bromoacetyl-3-arylsydnones with N'-(phenylmethylidene)carbonohydrazide. 4-Bromoacetyl-3-arylsydnones were in turn obtained by the photochemical bromination of 4-acetyl-3-arylsydnones (Kalluraya et al., 2003).

Experimental
To a solution of 4-bromoacetyl-3-(p-anisyl)sydnone (0.01 mol) and N'-(phenylmethylidene) carbonohydrazide (0.01 mol) in ethanol, catalytic amount of anhydrous sodium acetate was added. The solution was stirred at room temperature for 2 to 3 h. The solid product that separated out was filtered and dried. It was then recrystallized from ethanol. Crystals suitable for X-ray analysis were obtained from 1:2 mixtures of DMF and ethanol by slow evaporation.

Refinement
H1N3 was located in a difference Fourier map and allowed to refined freely. The remaining H atoms were positioned geometrically and refined using a riding model with C-H = 0.93 or 0.97 Å and U iso (H) = 1.2 U eq (C). The highest residual electron density peak is located at 0.68 Å from C13 and the deepest hole is located at 0.71 Å from S1. Fig. 1. The molecular structure of the title compound showing 50% probability displacement ellipsoids for non-H atoms and the atom-numbering scheme.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > 2sigma(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.